1. Related Application
The subject matter of this application is related to the subject matter of U.S. patent application Ser. No. 08//269,666, now abandoned, entitled "EVERYTHING CANNULA APPARATUS AND METHOD" filed on Jul. 1, 1994 by Albert K. Chin. The above application having the same assignee as the present invention and is incorporated herein by reference in its entirety.
2. Field of the Invention
The present invention relates generally to a dissection cannula assembly used for forming an elongated cavity in tissue planes particularly along the course of a small blood vessel. The present invention relates specifically to an assembly having multiple cannulae and balloons.
3. Description of Background Art
Present methods for the formation of an elongated cavity involve the use of blunt probes that are pushed through body tissue to accomplish the dissection. The force exerted by the passage of mechanical probes may lead to blood vessel avulsion and trauma to tissue and internal organs.
The problem becomes acute when dissecting and harvesting blood vessels having a small diameter of about 3 to 8 mm. The techniques which are used for dissection of larger blood vessels such as the aorta are not applicable. The aorta is located in the retroperitoneum, bounded by the peritoneum on one side and the psoas muscle on the other side. An everting balloon placed in the infrarenal space located just below the kidney will track easily down the length of the aorta along a natural cleavage plane when inflated.
An everting type of balloon experiences difficulty in dissection when applied to smaller diameter vessels. This is due to the greater adhesion that exists between small diameter blood vessels and the tissue that surrounds these vessels, as compared with the aorta and the tissue that surrounds the aorta. For example, if an everting balloon is placed adjacent to the saphenous vein in the leg, it usually squirts off in either direction upon inflation rather than track along the vein. This is due to the greater adhesion between the saphenous vein and the muscle that surrounds the vein.
Several balloon catheters are disclosed in various issued patents and publications. Exemplary everting balloon catheters used for arterial dilation include U.S. Pat. No. 4,479,497 (Fogarty et al., Oct. 30, 1984), U.S. Pat. No. 4,863,440 (Chin, Sep. 5, 1989), U.S. Pat. No. 4,696,304 (Chin, Nov. 29, 1987), and U.S. Pat. No. 4,630,609 (Chin, Dec. 23, 1986).
Double lumen everting balloon catheters, such as those disclosed in the Fogarty et al. '497 and the Chin '440 patents, have a through-lumen that permits the passage of an endoscope. However, an endoscope used in conjunction with those disclosed catheters in unable to monitor the dissection process, since the endoscope lies within the central lumen proximal to the everting balloon. As the balloon everts from the catheter, the internal inflation pressure squeezes the walls of the balloon and closes off the distal viewing channel. Also, the area that requires monitoring during balloon dissection is located at the advancing front of the everting balloon. This area corresponds to the balloon/tissue interface subject to forces that cause tissue separation. Thus, an endoscope in the central lumen of existing double lumen everting balloon catheters is unable to view the tissue separation area, since a double layer of balloon membrane lies between the endoscope and the tissue blocking the endoscopic line of sight. This double layer obscures and distorts the viewing image.
The catheter disclosed in the Chin '304 patent includes an outer catheter and an inner catheter slidably mounted within the outer catheter lumen. The inner catheter is provided with an inflatable balloon which is used to occlude an artery and it makes a pressure measurement through a separate lumen. The inner catheter is advanced through the outer catheter until the inflated balloon occludes the artery.
The dilatation catheter disclosed in the Chin '609 patent includes a double balloon system at the distal end of the catheter. The more distal of the two balloon elements is an everting type. In close proximity is a second balloon element of the sleeve type. By the eversion action of the distal inverted balloon, the catheter works its way into a stenosis zone with a minimum tendency to dislodge plaque and form an embolus. The proximal sleeve balloon is inflated to prevent the catheter from backing out of the artery upon eversion of the distal balloon through a fight stenosis.
Other versions of balloon dissection cannulae are commercially available, for example, from Origin Medsystems, Inc., the assignee herein. One such version uses a spherical, elastomeric balloon, and another such version uses a generally elliptical, inelastic balloon that is rolled up outside the lumen. These cannulae dissect generally spherical cavities.